Early and late insulin response as predictors of NIDDM in Pima Indians with impaired glucose tolerance

Summary Risk factors predicting deterioration to diabetes mellitus were examined in 181 subjects with impaired glucose tolerance. Fifty-seven subjects had impaired glucose tolerance on one occasion followed by normal glucose tolerance at a repeat oral glucose tolerance test, and 124 subjects had impaired glucose tolerance on two successive oral glucose tolerance tests. Subjects were followed for a median period of 5.0 years (range 1.0–17.2). The age- and sex-adjusted cumulative incidence of diabetes at 10 years of follow-up was higher in subjects who had impaired glucose tolerance on both tests (70%) than in those whose glucose tolerance was normal at the repeat test (53%), rate ratio (RR)=1.6, 95% confidence intervals (CI)=1.0–2.5]. Proportional hazards analyses were used to identify baseline risk factors (measured at the repeat oral glucose tolerance test) for subsequent diabetes, and incidence rate ratios were calculated for the 90th percentile compared with the 10th percentile of each continuous variable for the whole group. In all subjects, in separate models, higher body mass index RR=2.0, 95% CI=2.2–9.9], high fasting serum insulin concentrations RR=2.4, 95% CI=1.4–4.2], and low early insulin response RR=0.5, 95% CI=0.3–0.8] 30 min after a glucose load were significant predictors for deterioration to diabetes. In a multivariate analysis which controlled for age and sex, 120-min post-load glucose, fasting insulin and late insulin response predicted diabetes. In subgroup analyses the predictors of diabetes were generally similar in subjects who had impaired glucose tolerance at only one test and those who had impaired glucose tolerance on both tests. These findings suggest that in those subjects with impaired glucose tolerance whose glucose tolerance has returned to normal, the risk of subsequent diabetes is high. Insulin resistance, impaired early insulin response, or both, are predictive of subsequent development of diabetes in Pima Indians with impaired glucose tolerance.Abbreviations IGT Impaired glucose tolerance - OGTT oral glucose tolerance test - NGT normal glucose tolerance - CV coefficient of variation